This project is directed at increasing our understanding of the mechanisms of regulation of replication and transcription in prokaryotic and eukaryotic genomes. As an example of a prokaryotic system we are studying the bacteriophage lambda. Both replication and late transcription in lambda start at (different) specific sites on the lambda DNA molecule. Mutations in such sites abolish the associated function and thus serve to identify the sites. Mutations in the replication site, called ori-, have been available for a number of years. We have succeeded in determining the nucleotide sequence of the ori site and several of these mutants. The next step is to determine how this site interacts with the apparatus of the cell. No mutations yet exist for the late transcription site, called P'R. We are therefore isolating such mutations which we plan to sequence. Eukaryotic regulation is much less well understood. It is not even completely clear whether specific sites like those in lambda exist. However, by introducing selected examples of eukaryotic genes into lambda we can begin to study such questions by the same techniques developed for prokaryotic systems. We are beginning to do this for several mammalian genes.